The invention relates to a planar semiconductor device or component having at least one Zener (Z)-diode and at least one further semiconductor component. The invention is of particular interest for a semiconductor device or component having two power transistors connected to one another in the form of a Darlington circuit and having a Z-diode connected between the collector and the base of one of the two transistors.
In a p.sup.+ n.sup.- n.sup.+ diode, the breakdown voltage depends on the doping concentration in the n.sup.- region and on the distance between the p.sup.+ and the n.sup.+ regions. Quantitative correlations are explained in, for example, "Physics of Semiconductor Devices" by S. M. Sze, 2nd edition, 1981, John Wiley & Sons, and illustrated therein in a graph on page 105. At a distance of 20 .mu.m and with a doping concentration of up to about 7.times.10.sup.14 cm.sup.-3 the breakdown voltage is about 400 V; as the doping concentration increases, the voltage decreases more and more. When the doping concentration is constant, for example about 10.sup.- cm.sup.-3, the breakdown voltage rises as the magnitude of the stated distance increases, and is, for example, about 250 V at a 10 .mu.m distance and about 1000 V at around 50 .mu.m distance.
The assignee of this application has for more than ten years now been selling a semiconductor component under the name of BUX 30 AV, comprising a Darlington circuit with integrated Z diode between collector and base of one of the two power transistors in the Darlington circuit. The breakdown voltage of the Z diode is determined by a structure using the punch-through effect. The voltage is here determined by the doping of a p.sup.- layer and the depth of an n.sup.+ layer adjoining the former layer. The fact that the depth of the n.sup.+ layer cannot be adjusted with very high precision means that the breakdown voltage is subject to a relatively high tolerance. A further drawback is that the p.sup.- layer must be generated separately.
A planar semiconductor component with a similar function to that described above, but without a Z diode, is described in EP-B-0 179 099. In the upper part of the component, a channel stopper region and the base regions of two power transistors of the Darlington circuit are provided. A charge carrier breakdown takes place between one of the base regions and the common collector region.
For most applications of planar semiconductor components with preset breakdown voltage of several 100 V, it is desirable for the breakdown voltage to be subject to as minor as possible production fluctuations. The distance determining the breakdown voltage, between the anode region or base region on the one hand and the cathode/collector region on the other hand, can however only be set with wider tolerances than those permissible for the breakdown voltage. Alignment is therefore always necessary. In the case of the component in accordance with EP-B-0 179 099, this alignment is achieved with the aid of a special field plate device.
The above shows that the requirement was expressed to provide a planar semiconductor component designed such that the breakdown voltage can be adjusted simply with low production tolerances.